The present invention related to brake regulators for motor vehicles which make it possible to reduce the pressure of the brake fluid in the brake circuit of the rear wheels with respect to that of the brake fluid in the brake circuit of the front wheels as a function of the vehicle load.
The invention relates more particularly to a load-controlled regulator of this type using a fluidic means connected, for example, to a hydrostatic cushion arranged close to the vehicle suspension system.
Brake regulators of this type are well known in the art. Conventionally, they comprise a first piston capable of translatory movement in a bore formed in the body of the regulator, under the effect of the fluidic means. This first piston is provided with a push rod which cooperates with the end of a second piston forming part of a valve, for example a ball valve, which is open in the rest position and controls the passage of the brake fluid between a work chamber of the master cylinder and the brake circuit of the vehicle's rear wheels.
Upon application of pressure to the brake fluid, at first, with the valve being open, the pressure is communicated entirely to the brake circuit. Then, when the pressure reaches a given value, the piston closes the valve by being slightly displaced. If the pressure in the master cylinder continues to rise, the valve opens and closes so as to increase proportionally the pressure in the brake circuit. When the regulator is controlled by the load, the push rod exerts on the second piston a force opposite to that exerted by the brake fluid and thus delays the closure of the valve as a function of the vehicle load.
Regulators of this type operate in a perfectly satisfactory manner. However, the pressure increase in the master cylinder causing the second piston, and, consequently, the push rod and the first piston, to move back counter to the fluid cushion results in a considerable increase in the value of the brake fluid pressure at which the valve normally closes, since everything happens as if the vehicle were under a greater load than it actually is, which is detrimental to safety as the rear wheels may then lock before the valve acts.